Intro to GI physiology

Question 1

What are the 6 basic functions of the GI tract?

Answer 1

Ingestion
Mechanical processing
Digestion
Secretion
Absorption
Excretion

Question 2

What does the peritoneum secrete and why?

Answer 2

Peritoneal fluid which provides lubrication and prevents friction between organs

Question 3

What is a volvulus?

Answer 3

Bowel gets twisted and blood supply is cut off - becomes ischemic or good can’t pass

Question 4

What is carried in the mesenteries?

Answer 4

Blood vessels
Nerves
Lymphatics

Question 5

Why are there fat pads on the mesenteries?

Answer 5

Cushion and protect organs

Question 6

What is the general structure of the epithelial cells in the gut?

Answer 6

Mucosa (innermost)
Submucosa - connective tissue
Musculares externa - circular muscle layer and longitudinal muscle layer that provide contraction fro peristalsis (myenteric plexus is between these two muscle layers)
Serosa - connective tissue containing a double layer of peritoneum

Question 7

Are epithelial cells polarised? why is this important?

Answer 7

Yes

Polarised cells can target proteins to discrete parts of the cell to determine where proteins are expressed

Question 8

What are tight junctions?

Answer 8

Near the apical surface of the cell, define apical and basolateral domain and stop proteins from mixing
Seals the gap between epithelial cells

Prevent the diffusion of plasma membrane proteins from apical to basolateral membranes of epithelial cells

Question 9

What are occulting junctions?

Answer 9

Main bit of the tight junction - prevents stuff from passing through

Question 10

What are adherens junctions?

Answer 10

Connects cells together by actin filaments

Question 11

What are desmosomes?

Answer 11

Connect adjacent cells together by filaments

Question 12

What are gap junctions?

Answer 12

Allow the passage of small water-soluble molecules from cell to cell

Question 13

What is in between the baso-lateral membrane of the epithelial cell and the capillary network?

Answer 13

Interstitial fluid

Question 14

What is flux?

Answer 14

Movement of molecules across the epithelium (either direction)

Question 15

How is flux measured chemically?

Answer 15

Using radioactive isotopes as tracers

Question 16

What causes flux?

Answer 16

Electrochemical gradients

Question 17

What is the equation for net flux of a solute?

Answer 17

Jnet = Jabs - Jsec

Jnet = net flux
Jabs = absorptive flux
Jsec = secretory flux

Question 18

What are the two routes for absorption from the lumen into the blood?

Answer 18

Transcellular (through cells)

Paracellular (between cells)

Question 19

What is secondary active transport?

Answer 19

Energy to drive active transport comes from the electrochemical gradient from one substrate (using primary active transport), and the second substrate then moves against its electrochemical gradient

Question 20

What cellular route must active processes use for absorption?

Answer 20

Transcellular

Question 21

Which route of absorption can water use?

Answer 21

Both paracellular and transcellular

Question 22

What channels does water move through to get across plasma membranes?

Answer 22

Aquaporin channels

Question 23

What type of nerves supply the main sensory and motor control of GI activity?

Answer 23

Parasympathetic

Question 24

What nerve controls the forget and midgut derivatives?

Answer 24

Vagus

Question 25

What nerve controls the hindgut components of the GI tract?

Answer 25

Pelvic splanchnic nerves

Question 26

What is the enteric nervous system?

Answer 26

Motor and sensory neurons (autonomic) in two interconnected plexuses (myenteric and submucosal) in the walls of the GI tract - these neurons control the coordinated contraction and relaxation of intestinal smooth muscle and regulate secretion and blood flow. Thousands of small ganglia that lie within the walls of the GI tract organs. Generally independent of CNS, but does receive input from sympathetic nerves

Question 27

What modulates the enteric nervous system?

Answer 27

ANS

Question 28

Where is the myenteric plexus of the enteric nervous system located?

Answer 28

Between the circular muscle and longitudinal muscle layer in the musclaris externa

Question 29

Where is the submucosal plexus of the enteric nervous system located?

Answer 29

Between the submucosa and the circular muscle layer

Question 30

What are slow waves?

Answer 30

Regular periodic depolarisations in the resting membrane potential of cells that makes it easier for a small signal to initiate a contraction/action potential. They set the timing for when contraction MAY occur. (a neural or hormonal signal will ONLY initiate activity during a slow wave)

Question 31

What regulates slow waves?

Answer 31

Myenteric and submocsal plexi

Question 32

How often do slow waves occur?

Answer 32

3-12min-1

Question 33

What is the role of interstitial cells of Cajal?

Answer 33

Mediate slow waves (pacemaker cells) Facilitate communication between nervous system and smooth muscle. Cause contraction in a rhythmic and coordinated fashion - peristalsis.